Study On Dynamic Heat Generation Model Of Lithium-ion Battery And Evolution Mechanism Of Temperature Inhomogeneity Of Battery Module

Due to the increasingly severe energy crisis and environmental pollution,electric vehicles have been developing rapidly in recent years.As the power source of electric vehicles,lithium-ion power battery has become one of the main factors which restricting the development of electric vehicles.Thermal performance not only has a direct impact on the performance and life of lithium-ion battery,but also relates to the safety of the vehicle.In order to meet the needs of the performance of electric vehicles,multiple single batteries are formed into battery module through series and parallel connection.In this case,the inconsistency between single batteries will lead to the decline of the performance and life of battery module,and also affect the thermal safety of battery.Therefore,it is particularly important to study the thermal performance of lithium-ion battery and the inconsistencies within the battery module.A 50 Ah prismatic lithium-ion battery was taken as the research object in this paper.The dynamic heat generation model was verified by temperature rise experiment of single battery and module.Based on this model,the influence mechanism of temperature inhomogeneity of parallel battery module on unbalanced discharge current was studied.The details are as follow.By disassembling the single battery,the necessary structural parameters were obtained to calculate the thermal properties of the battery.An experimental platform was built to test the temperature rise characteristics of the battery and the internal resistance of charge and discharge and the temperature coefficient of the open circuit voltage and the open circuit voltage.The results show that the charging internal resistance and the discharging internal resistance of the battery have a certain difference in change trend,and the overall value is also different.The temperature coefficient of the open circuit voltage can be positive or negative,showing a highly nonlinear trend.Based on the parameters obtained from the experiment,the dynamic heat generation model of the single battery was established.The temperature rise of single battery under the ambient temperature of 10℃,20℃,30℃,40℃,constant discharge of 1 C and 0.5 C and dynamic discharge was simulated.Comparing with the experimental data,the result show that the model is accurate enough.A 3-parallel 4-series battery module was manufactured and its temperature rise characteristic was tested.By testing the internal resistance of the battery module,the welding resistance was measured indirectly.Based on kirchhoff’s law of current and voltage,the current of each branch in the parallel module was solved.A three-dimensional dynamic heat generation model of the battery module was established which can consider the influence of inconsistencies on current and heat generation.The simulation data was compared with the experimental data.And the accuracy of the dynamic heat generation model was verified.The evolution mechanism of unbalanced discharge current under the condition of uneven temperature distribution,different initial capacity and the simultaneously existence of uneven temperature distribution and different initial capacity in the parallel module was simulated.The results show that the unbalanced discharge current has different distribution rules under different inconsistent conditions,and the inconsistent parameters will restrict each other and affect the current distribution in the parallel battery module.